Apoptosis is a phenomenon essential to the physiological process of removing unnecessary cells or damaged cells and maintaining the number of normal cells in vivo. Owing to progress in elucidation of the fact that the regulatory mechanism of apoptosis is often impaired in cancer or immune diseases and also elucidation of the regulatory pathway of apoptosis, the development of a novel apoptosis inducer which can be used in the treatment of cancer or immune diseases has been advanced. In particular, an antibody which has a binding affinity for a ligand for a cell surface receptor involved in apoptosis induction typified by a death receptor or an antibody which has a binding affinity for said death receptor is expected to have a therapeutic effect on these diseases (see, for example, Non-patent document 1). Death receptor 5 (DR5) which is one of the death receptors is sometimes also called KILLER, TRICK 2A, TRAIL-R2, TRICK B, or CD262, and a plurality of agonistic antibodies which induce apoptosis in cells are known (see, for example, Non-patent document 2 or 3, or Patent documents 1 to 6). Some antibodies are currently being developed in clinical trials as candidate therapeutic agents and are expected to have a therapeutic effect such that the antibodies specifically act in an agonistic manner on cells (cancer cells or immune disease-related cells) which express the receptor in order to kill the cells. In order for such an antibody to have an antitumor effect, it is essential that the cells express DR5, however, it has been revealed that there is no correlation between the effect and the expression level of DR5 in a preclinical trial (Non-patent document 4). It is considered that this is because a cellular response is regulated by many factors such as the expression level of intracellular signaling molecules (such as caspase-8 or Bcl-2) involved in apoptosis pathways (Non-patent document 5).